FIG. 8 is a schematic cross-sectional view of a Barfield-type constant velocity universal joint (hereinafter referred to as “constant velocity universal joint”) 10 which has heretofore been known. The constant velocity universal joint 10 has an outer member 12, an inner member 14, and rolling balls 16 interposed between the outer member 12 and the inner member 14.
The outer member 12 has a shank 18 and an open tubular member 20. The tubular member 20 has six angularly equally spaced ball grooves 22a through 22f defined in a curved inner wall surface thereof.
The inner member 14 is held by a retainer 24 and inserted in the tubular member 20. As shown in FIG. 9, the inner member 14 has as many inner ball grooves 26a through 26f as the number of the ball grooves 22a through 22f in the outer member 12, the inner ball grooves 26a through 26f being defined in a curved outer circumferential surface of the inner member 14 which projects radially outwardly. The inner member 14 also has a through hole 27 defined therein which extends from one end to the other end thereof. A drive shaft DS is fitted in the through hole 27.
The retainer 24 has windows 28 defined therein which extend from an inner wall surface to an outer wall surface thereof. The rolling balls 16 are accommodated respectively in the windows 28 and are inserted in the ball grooves 22a through 22f in the outer member 12 and the inner ball grooves 26a through 26f in the inner member 14.
If the central line L of the constant velocity universal joint 10 and a line drawn from the center of one of the balls 16 toward the central line L vertically cross each other at a point C, then it is ideal that the point A at the center of curvature (r) of the inner ball grooves 26a through 26f and the point B at the center of curvature (R) of the ball grooves 22a through 22f are spaced from the point C respectively, by equal distances, i.e., AC=BC is satisfied, or in other words, the point A and the point B are offset from the point C respectively, by equal distances. The point A is referred to as the center of a spherical inner surface, and the point C as the center of ball grooves.
The dimensions of inner members 14 that are successively produced by forging are not necessarily identical to each other, but tend to vary from reference values. Stated otherwise, AC=BC may not necessarily be satisfied.
Therefore, it is customary, for example, to measure the distances from an end surface of the inner member 14 (a surface facing a closed end surface in the tubular member 20 of the outer member 12) to the point A and the point B, and select the inner member 14 as a proper inner member if the measured distances fall within preset allowable ranges and select the inner member 14 as an improper inner member if the measured distances fall outside of the preset allowable ranges. Patent documents 1, 2 propose dimension measuring apparatus for use in such measurements.
The selecting process is also carried out in processes subsequent to the forging process, e.g., in a heating process and when a machining process such as a cutting process is finished.
A plurality of outer members 12 are also successively produced by forging. Consequently, as with the inner members 14, the dimensions of the outer members 12 are not necessarily identical to each other, but somewhat vary from reference values. It is also customary, after the forging process, the heating process, and the cutting process, etc. are finished, to measure the distances a, b from the closed end surface in the tubular member 20 to the point B and the point C, as shown in FIG. 8, subtract the distance a from the distance b to calculate an offset, and select the outer member 12 as a proper outer member if the offset falls in a preset allowable range and select the outer member 12 as an improper outer member if the offset falls outside of the preset allowable range.
Known apparatus for measuring the dimensions of outer members are described in Patent documents 3, 4 in addition to Patent document 1.
Patent document 1: Japanese Laid-Open Utility Model Publication No. 57-68505;
Patent document 2: Japanese Laid-Open Utility Model Publication No. 56-97701;
Patent document 3: Japanese Laid-Open Utility Model Publication No. 58-6205; and
Patent document 4: Japanese Laid-Open Utility Model Publication No. 56-169202.